The present invention relates to acoustic ink printing (xe2x80x9cAIPxe2x80x9d). It finds particular application in conjunction with reducing the number of passes a printhead makes of a swath for increasing the speed at which an image is printed, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Various fluid application technologies, such as printing technologies, have been developed. One such printing technology uses focused acoustic energy to eject droplets of marking material from a printhead onto a recording medium. This printing technology is known as acoustic ink printing (xe2x80x9cAIPxe2x80x9d). Printheads used in AIP devices typically include a plurality of droplet ejectors, each of which launches a converging acoustic beam into a pool of fluid (e.g., liquid ink). The angular convergence of this beam is selected so that the beam focuses at or near the free surface of the ink (i.e., at the liquid-air interface). Printing is performed by modulating the radiation pressure that the beam of each ejector exerts against the free surface of ink to selectively eject droplets of ink from the free surface.
Color printing is typically achieved by ejecting droplets of various colored inks from respective printheads. Varying numbers of droplets of the various colored inks are mixed to produce a wider gamut of colors. For example, inks of four (4) colors (e.g., cyan, magenta, yellow, and black (xe2x80x9cCMYKxe2x80x9d)) are mixed to achieve a variety of colors in the CMYK gamut. The speed at which a printed output is produced is a function of the number of passes the printhead makes over the printing medium. More than one (1) pass is necessary when any one of the printhead ejectors does not deliver the needed ink to a given location (i.e., when any one of the printheads does not deliver enough of its ink to achieve the desired color at a specific pixel location) before the printhead moves out of range. Until now, there has been no means for controlling the number of droplets ejected from an AIP device printhead for reducing the printing time while maintaining a desired quality of the printed output. In fact, current AIP devices typically pass the printhead over the printing medium at least twice, regardless of the number of droplets that need to be ejected to achieve the desired color and/or quality.
In conventional ink-jet printing, various approaches have been used to control the number, overall pattern, size, and spacing of individual ink droplets (xe2x80x9cdotsxe2x80x9d) ejected from the ink-jet printhead and printed within a given surface area of media in order to control the print quality of the printed media. This is desirable to ensure that the droplets printed during one (1) xe2x80x9cpassxe2x80x9d of the ink-jet printhead relative to adjacent print media have adequate time to dry before another overlying pass is made over the same printed area.
Inadequate drying time of the droplets produces a number of undesirable characteristics in resultant print quality, depending upon the type of print media used. For example, in the field of color ink-jet where ink colors such as cyan, yellow, and magenta are printed over a given area in dot-on-dot (xe2x80x9cDODxe2x80x9d) fashion, excessive volumes of ink per unit area may be produced on the printing medium. Such excessive volumes cause the ink to bead-up and/or coalesce as a result of an over-saturation of ink on some areas.
In addition to having adequate time to dry, it is also desirable that dots of different passes, and within a given pass, dry uniformly and consistently. Non-uniform or inconsistent drying produce a number of undesirable print quality effects depending upon the media used. Inadequate drying time is one possible cause of non-uniform drying of the ink.
In an effort to avoid the above problems of beading, coalescence, and over-saturation using DOD printing, some color ink-jet printers implement dot-next-to-dot (xe2x80x9cDNDxe2x80x9d) printing processes. DND processes eject dots onto side-by-side pixels in a given printed area. DND printing processes typically require the printhead to pass over a swath of the printing medium more than one (1) time. In fact, the printhead in a conventional ink-jet printing device may make several passes over the swath. These pixels may, for example, form quadrants or other sections of a larger or super pixel as is known in the art, and color mixing takes place at the side or DND interface boundaries within the super pixel. This DND approach to color ink-jet printing is preferable to DOD printing processes where either large ink drop volumes (e.g., above about 20 pico-liters) or largely water based inks, or both, are used in printing on plain paper.
Another approach to solving the above problems in ink-jet printers is to produce complementary multiple-pass DOD ink-jet printing processes. In this approach successive multiple passes of an ink-jet printhead relative to the print media in a DOD process are performed so that a first ink swath is completed by the use of two successive ink passes. Each pass has dot patterns that are complementary to each other. Thereafter, a second swath is laid down immediately adjacent to the first swath. Like the first swath, the second swath is completed by the use of two successive ink passes having complementary dot patterns therein.
Although the approaches discussed above overcome some problems in ink-jet printers, they have other drawbacks and/or may not be appropriate for AIP devices. For example, while the DND approach works for devices producing drops having large ink volumes, it is not as beneficial for printing devices that produce relatively small drops. Because AIP devices are capable of producing drops of about five (5) pico-liters, or even two (2) pico-liters, the DND approach does not achieve the same benefits in AIP devices that are achieved in ink-jet printers. Furthermore, while the multiple-pass DOD ink-jet printing processes reduce beading, it may produce banding at the boundaries between adjacent print swaths.
Therefore, none of the above ink-jet printing processes are suitable for increasing the speed AIP devices while maintaining a desired quality of the printed output.
The present invention contemplates a new and improved AIP device and method which overcome the above-referenced problems and others.
An apparatus ejects droplets of at least one fluid onto a printing medium. At least one printhead stores a respective one of the at least one fluids. The droplets are ejected from the respective printheads. A processor, electrically connected to the means for ejecting the droplets, causes the droplets to be ejected from the printheads for minimizing a number of scans each of the printheads makes over a plurality of swaths on the printing medium.
In accordance with one aspect of the invention, each of the means for ejecting the droplets is associated with at least one pixel in the swath on the printing medium.
In accordance with a more limited aspect of the invention, the processor determines a maximum number of droplets that are capable of being ejected from each of the ejecting means during one of the scans for at least one of the pixels in the swath. The processor determines a desired number of droplets of each of the fluids to eject from the respective printheads for achieving a desired color in each of the pixels. Then, the processor determines an actual number of droplets of each of the fluids to eject from the respective printheads for minimizing the number of scans each of the printheads makes over the swath. The processor determines the actual number of droplets as a function of the desired number of droplets.
In accordance with an even more limited aspect of the invention, four printheads eject the droplets of four respective fluids having different colors.
In accordance with another aspect of the invention, the printheads eject the droplets of fluids including cyan, magenta, yellow, and black colors.
In accordance with a more limited aspect of the invention, the maximum number of droplets ejected from each of the ejecting means during one of the scans is five.
In accordance with an even more limited aspect of the invention, if the desired number of droplets for any of the fluids ejected from any of the printheads in the respective swath is greater than the respective maximum number of droplets, the actual numbers of droplets ejected from the printheads equals the respective maximum number of droplets.
In accordance with another aspect of the invention, if any of the actual numbers of droplets is greater than the respective maximum number of droplets, the respective ejecting means ejects the respective maximum number of droplets during a single one of the scans.
One advantage of the present invention is that it reduces the number of scans a printhead makes of each swath of a printing medium.
Another advantage of the present invention is that it increases the speed at which the pixels are printed on the printing medium.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.